Czochralski method is a representative method for the growth of a single crystal from a melt.
Czochralski method uses a crucible 2 provided in a closed chamber 1 as shown in FIG. 1. The crucible 2 is supported by a support 3 so that the crucible 2 is capable of rotation and/or vertical motion. There are concentrically disposed a heater 4 and a heat insulator 5 around the crucible 2.
A raw material is received in the crucible 2 and intensively heated by the heater 4 to prepare a melt 6. The melt 6 is held at a temperature suitable for the growth of a single crystal.
When a seed crystal 7 being hung from a rotary winder 10 through a wire 9 is brought into contact with the melt 6, a single crystal 8 grows on the seed crystal 7 so that the crystalline orientation of the seed crystal 7 is transferred to that of the growing crystal 8. The seed crystal 7 is then rotatingly pulled up in response to the growth of the single crystal 8. The crucible 2 is descendingly rotated by the rotating motion of the support 3, too.
The obtained single crystal 8 is sliced to wafers useful as substrates for electronic devices.
When the melt 6 to which Sb is added as a type-n dopant is used for crystal growth, an obtained single crystal 8 is useful as a high-conductivity semiconductor material bcause of containing Sb. Oxygen originated in SiO.sub.2 dissolved from the crucible 2 into the melt 6 is included in the single crystal 8, too.
Oxygen atoms included in the single crystal 8 precipitate in a bulk and form crystalline faults, when the single crystal 8 is heat treated. The crystalline faults are utilized as a gettering center for capturing heavy metal impurities remaining on the surface of a semiconductive single crystal substrate comprising an electronic device. Hereby, the heavy metal impurities are made harmless. Dissolved oxygen atoms are effective for enhancing the strength of the single crystal substrate, too. In this regard, it is preferable to increase oxygen concentration in the melt, in order to increase an amount of oxygen included in the single crystal 8. However, it is difficult to keep the oxygen concentration in the melt at a high level under a stable condition.